<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>动态改变样式文件</title>
    <script >
        window.onload = function () {
            let css1 = document.getElementById("css1"); 
            css1.onclick = function () {
                document.getElementById("bottom").style.fontSize="24px";
            }
        }
    </script>
    <script>
        $().ready(function () {
            $("#css2").click(function () {
                $("#bottom").attr("任务1-3(css2).css");
            });
        });
    </script>
</head>
<body>
    <div id="bottom">
        Copyright&nbsp;© &nbsp;2020-2021 17sai.com 
        All Rights Reserved.&nbsp;FL&nbsp;版权所有&nbsp;&nbsp;&nbsp;&nbsp;切换样式
        <span style="cursor: pointer;" id="css1">应用css样式1</a>|<span style="cursor: pointer;" id="css2">应用css样式2</a>
        
    </div>
</body>
</html>